Re: RFC: Starting a stable kernel series off the 2.6 kernel

Rob Landley
2005-12-06T03:17:19Z

On Sunday 04 December 2005 23:59, Luke-Jr wrote:
> On Sunday 04 December 2005 23:22, Greg KH wrote:
> > On Sun, Dec 04, 2005 at 04:46:31AM +0000, Luke-Jr wrote:
> > > Well, devfs does have some abilities udev doesn't: hotplug/udev
> > > doesn't detect everything, and can result in rarer or non-PnP devices
> > > not being automatically available;
> >
> > Are you sure about that today?
>
> Nope, but I don't see how udev can possibly detect something that doesn't
> let the OS know it's there-- except, of course, loading the driver for it
> and seeing if it works.

Stuff shows up in /sys whether or not Linux has a driver loaded for it.

ls -l /sys/bus/*/devices

Hotplug insertion events are for when the _device_ shows up, not for when the
driver is loaded.

> > And udev wasn't created to do everything that devfs does.
>
> Which might be a case for leaving devfs in. *shrug*

I think it was a polite way of saying "udev doesn't suck, have unfixable
races, randomly crash your system..."

> > What information are you talking about here?
>
> I'm assuming everything in /etc/udev/rules.d/50-udev.rules used to be in
> the kernel for devfs-- perhaps it was PAM though, I'm not sure.
> Other than that, I don't expect that simply installing a new kernel module
> will allow the device to be detected automatically, but that some hotplug
> or udev configurations will need to be updated also.

On an unrelated note, the proposed file format for busybox's mdev looks
something like:

hd[a-z] 0:3 700
hd[a-z][0-9]* 0:3 740
.* 0:0 700

There's a little more to it than that, but really, specifying ownership and
permissions is all we _really_ care about. (We're not trying to obsolete
udev.)

The point is, 90% of the complexity of udev is optional. This _can_ be a lot
simpler if you're not trying to tackle strange persistent naming issues
resulting in dynamically generated symlinks, and similar fun. (Which we may
add the ability to do as compile-time config options later, but perhaps not
until somebody actually misses them...)

We really don't forsee having to update mdev for deal with new kernel
versions... ever, if we can help it.

And a dynamic module loader hanging off of /sbin/hotplug is probably
(conceptually) a different tool from mdev...

Rob
--
Steve Ballmer: Innovation! Inigo Montoya: You keep using that word.
I do not think it means what you think it means.